class_docstr: Base class for feeds.
  
  :param maxLen: The maximum number of values that each :class:`pyalgotrade.dataseries.DataSeries` will hold.
      Once a bounded length is full, when new items are added, a corresponding number of items are discarded
      from the opposite end.
  :type maxLen: int.
  
  .. note::
      This is a base class and should not be used directly.
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docstr: Returns the event that will be emitted when new values are available.
  To subscribe you need to pass in a callable object that receives two parameters:
  
   1. A :class:`datetime.datetime` instance.
   2. The new value.
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code: def getNewValuesEvent(self):
      """Returns the event that will be emitted when new values are available.
      To subscribe you need to pass in a callable object that receives two parameters:
  
       1. A :class:`datetime.datetime` instance.
       2. The new value.
      """
      return self.__event
  
file_path: pyalgotrade/pyalgotrade/feed/__init__.py
imports: import abc
  from pyalgotrade import observer
  from pyalgotrade import dataseries
label_desc: Use image node_id 8 for calling the BaseFeed obj's underlying member method code with example usage: obj.getNewValuesEvent() and returns: self